The present invention relates to bicycles and more particularly to a multi-speed sprocket assembly including a larger sprocket having first and second support points configured to bend a shifting chain segment at first and second angles, respectively.
Typically, a bicycle having a derailleur shifting system includes a drive multi-speed sprocket assembly, a driven multi-speed sprocket assembly and a chain extending therebetween. The derailleur axially moves or shifts the chain between sprockets. To facilitate the shifting of the chain from a smaller sprocket to a larger sprocket, the sprockets may have teeth missing that form missing-tooth gaps and recesses on a face of the larger sprocket facing the smaller sprocket. However, one disadvantage of providing missing-tooth gaps is that if several missing-tooth gaps are disposed on one sprocket, it cannot be ensured that the chain transitional segments from one sprocket to the other sprocket are identical. For example, if the number of teeth of the larger sprocket, including the missing teeth, is not integer divisible by the difference between the tooth number of the larger sprocket and the adjacent smaller sprocket then, in the case of two missing-tooth gaps on the larger sprocket, at least one missing-tooth gap may not be positioned such that it is optimally offset relative to the smaller sprocket.
The chain transitional segment may be defined as the distance between the contact point of the chain roller on the last tooth of the smaller sprocket and the contact point of the chain roller on the tooth of the larger sprocket that follows the tooth gap. An optimum transitional segment exists when the chain roller on the tooth of the larger sprocket is in an optimum support position (AP) which causes the subsequent chain roller to neither “ride” on a tooth tip of the larger sprocket nor swivel excessively farther from the load tooth flank toward the larger sprocket. An optimum transitional segment ensures smooth shifting of the chain from the smaller sprocket to the larger sprocket.
With an optimum transitional segment, the chain engages the sprockets at three points. One chain roller rests against the last tooth of the smaller sprocket, one chain link plate is laterally supported on the run-on ramp on the larger sprocket and another chain roller rests against the no-load tooth flank in the optimum support position (AP) and makes contact with that tooth of the larger sprocket that follows the missing-tooth gap. If the support position is too high relative to the optimum AP or is displaced in the direction of the tooth tips, a noticeable jerk occurs during the shifting process because the chain roller contacts the larger sprocket to far away from the load tooth flank and jerkily compensates for this distance. If the support position is too deep relative to the optimum AP or displaced in the direction of the tooth base, then the shifting process is delayed. Under high load, in particular, there occurs a “riding” of the chain since the chain rollers slip so far in the direction of load that they no longer engage the larger sprocket, but instead only rest on the tooth tips. At the moment when the smaller sprocket releases the chain, the chain snaps, with strong jerks, into the intermediate space on the larger sprocket or causes the corresponding chain rollers to strike against the load tooth flanks. This may result in overload and increased wear on the corresponding components of the drive train.